Various detectors and systems have been developed to detect and indicate the presence of particles of combustion, or of a fire, or of an increase in temperature. Such systems generally use two or more conductors between a control panel or control unit, which is coupled to the individual detectors. In general, the individual detectors determine when an undesired condition is present, by comparing some parameter (such as current flow or voltage level) with a predetermined reference value. When the detector determines the reference value has been exceeded, the undesired condition is present and the detector latches in the alarm condition. Generally the control unit does not know the precise location of the alarmed detector, and after three or more detectors have gone into alarm on one zone, cannot recognize how many detectors are in the alarmed condition on that zone.
Prior art detectors generally are not capable of having their sensitivity checked from the control panel over a two-wire loop, or having their sensitivity adjusted from the control panel without taking the stem out of operation.
A serious shortcoming of prior art systems is that loop continuity is supervised, but detector presence and/or operation is not supervised. If any detector is removed and replaced by a cardboard form or some other mechanical unit to simulate detector presence, continuity along the conductor pair is maintained and the control unit does not "know" that the detector is in fact missing from the area.
Several of these shortcomings were overcome in the system described and claimed in the earlier application noted above. That system includes a bidirectional, interactive fire detection system in which only a single conductor pair is required. The control panel (or controller) selectively addresses the individual transponders, and each transponder responds when addressed. The controller also issues command signals to the addressed transponder, which command signals represent desired functions or actions to be taken by the selectively addressed transponder, which then accomplishes the functions or actions. Such command signals can control the operation of various devices coupled to the transponder, such as relays, visual and/or audible indicators, or any other device.
In the system described in the earlier application the transponder returns a signal which identifies the type of transducer associated with that transponder. For example, the transducer could be an ionization detector, a photoelectric detector, alarm-causing switches (such as a manual pull station or a thermal switch), non-alarm-causing switches (such as an abort control for Halon, or day-night switches) or a complete zone of detectors. This return signal is termed the "identification response".
The transducer also returns a "transducer response", a signal from which the controller determines the transducer sensitivity. Successive transducer response signals can be recorded to provide a continuing record of transducer sensitivity, as described in the earlier application. In the system of this invention, it is desirable to compensate for changes in the transducer response signal.
Even with the significant improvements just described in connection with the earlier system, there are areas in which such a bidirectional, interactive system can be further improved. It is highly desirable that the transponder return a reference signal from which the controller can determine that the transponder is functioning properly. This signal will be referred to as the "calibration response". In addition, it is desirable that the system be equipped to compensate for changes in the calibration response signal, and further that at least certain transducers be capable of selective and remote calibration.
Also very important is that the transponder return signal, the "transducer response" from which the controller determines the transducer sensitivity, be used in a manner to provide adjustable sensitivity of the transducer.
Another important consideration is that the improved system be useful to control a multi-zone system.
In addition, where a plurality of zones are coupled to the same two common terminals, it is desirable to identify the separate zones one from another. The "identification response" signal can be used to provide this identification of the individual zones.
Another significant consideration is that the controller of the system should be able to "read through a short", that is, discern usable and significant information when a transponder is replying over the conductor pair, even though one or more additional transponders may inadvertently have its output fail in an open or shorted state when the addressed transponder is replying.
Yet another important consideration is that the system be able to poll the transponders at a time when the controlled premises are substantially unoccupied and quiescent (for example, 2:00 a.m. Sunday), to obtain and/or store various reference data.
Another desirable advantage of the improved system is that it be able to identify the precise location of a break in one wire of the conductor pair.
Another important consideration of the improved system is that it be able to measure the analog representation of the signal returned from the transponder with a greater accuracy than would be possible with a simple, coarse measuring arrangement, without imposing the requirement of greater accuracy on the system over the entire information-return time interval.
Yet another important consideration is that the new system be capable of providing a compensation signal to the controller as a function of various conditions, such as component aging, wind velocity, temperature, humidity, supply voltage at the associated transducer, and so forth.
A bidirectional, interactive system for detecting and indicating a predetermined condition, such as the presence of fire or products of combustion, when constructed according to the teaching of the earlier application, need employ only two conductors. A controller and a plurality of transponders are each coupled to the same conductor pair, without any need for an end-of-line resistor or other termination unit, or without any other means for supplying power to the transponders and/or transducers. The controller sends out a series of signal groups or sets, with each signal group addressing a particular transponder. One or more of the signals in a given group can be modified by the controller to pass information to the addressed transponder. Each transponder has a unique address and, when it recognizes its own address, can return information to the controller by modifying some characteristic of one signal directed back to the controller. It is important that each transponder does not depend on the proper operation of the other transponders for receiving or sending information. Each transponder can return information concerning the identification and condition of associated transducers.